Conventional screwdrivers, electric and hand-operated, have various types but are same in one point that the twisting force exerted on the twisting rod is fixed, i.e. the torque of the twisting rod is set at the factory and within the fixed torque the operator should use the screwdriver empirically. Generally, the screwdriver can function very well but in special cases, it still will make many troubles, such as:
1. When it is used to tighten the screws of precision machinery which requires greater accuracy in connection of parts and has components with moderate hardness and strength, it would impair the designed connection or cause damage to the components if too much pressure is exerted. These are always the case because the operator of a conventional screwdriver can only exert the pressure by experience.
2. In removing screws, the user often does not know the torque required for a tightened screw, or the increased torque for a rusty screw, and can not select a screwdriver with an appropriate end to fit into the slot in the head of the screw to be removed. As a result, it would take more trouble to turn the screw or damage would be caused to the screw or the screwdriver end.
In view of the above mentioned disadvantages, the inventor who has years of experience in making tools of the kind tried to make new designs and improvement, and developed this invention after many tests and experiments. By using the spring-adjusted engagement of the toothings of the twisting rod and the handle block, the twisting force exerted by the twisting rod of the screwdriver of the present invention during screw tightening or loosening can be adjusted and the convenience and application of the screwdriver to precision machinery is greatly increased.
The main object of this invention is to provide a screwdriver with an adjustable engagement of toothings which changes the fixed torque of the conventional screwdriver to a wide range of torque from 5-90 Kgs to meet the need of various torque required in tightening and loosening screws of precision machinery.
Another object of this invention is to provide a screwdriver of which the torque can be set at will in the operation of tightening and loosening screws. If the set torque is exceeded, the twisting rod will slide automatically.
Still another objective of this invention is to provide a screwdriver of which the torque can be set within a wide range for a variety of applications in precision operation.
A further object of this invention is to provide a screwdriver which will not cause damage to the screw, working piece or the end of the screwdriver itself when it is used to turn screws.